Currently, a disproportionately large percentage of the cost associated with the production of optical communication packages is taken up with the high precision alignment that is required between micron-sized optical elements within the module such as laser diodes and single-mode fibres. Due to the high degree of positional accuracy that must be achieved, relatively slow labour intensive techniques are often used for producing such packages. This slow and costly approach is a major obstacle to the production of low cost telecommunication equipment. Alternatives to this approach have been proposed and/or implemented.
One alternative approach provided by Axsun Corporation of Billerica, Mass., USA utilizes specialized deformable microelectromechanical systems (MEMS) submounts for each of the components. These submounts are placed with a pick and place machine on the substrate and bonded in place. Subsequently, very precise positioning of the submount is achieved with the use of a specialist robotic arm which applies a force to the submount to deform it in a known manner such that the desired position or alignment is achieved. This technique suffers from a large initial investment, long assembly and set-up times. Moreover, the large variety of small volume components typically used to build specialized equipment limits the cost-effective use of this approach. In addition, this technique relies heavily on known tuning curves which are specific to the customized sub-mount making this technique inflexible in regard to adapting it to different devices.
Several studies investigate the use of MEMS thermomechanical actuators for sub-micron positional control of optical fibers (See for example, R. R. A. Syms, H. Zou, D Uttamchandani, J. Stagg, J. MicroMech. Microeng. 14 1633 (2004), Active Fiber Optic MEMS Aligner Boeing—U.S. Pat. No. 5,553,182) The methods described in these studies allow small adjustments of the position of a fiber end to improve coupling efficiency with a light source or another fiber. Furthermore, Lin et al. (L. Y. Lin, J. L. Shen, S. S. Lee, M. C. Wu, IEEE Photon. Tech. Lett. 9, 345 (1997)) have demonstrated the use of MEMS electrostatic actuators in XYZ stages for free space beam steering.
The major disadvantage of the first two approaches to optical package manufacture described above is one of cost, both being labor and/or capital intensive. In addition, both of these techniques are limited in their diversity because they both use external manipulation to alter the position of the component.
The MEMS devices also have significant disadvantages associated with them. The fiber positioning devices are capable of moving a single fiber in only one direction and for only a small distance, on the order of twenty micrometers. The method proposed by Lin et al. suffers from high cost, complexity and reliability issues. Finally, the MEMS based devices which operate using electrostatic actuation have high voltage requirements and they are typically capable of only small displacements. The MEMS devices operating on the basis of a thermomechanical response typically dissipate a considerable amount of energy of the order of 0.3 watts per micron of displacement.